The present invention is in the field of thin-film deposition, such as Chemical Vapor Deposition (CVD) and Plasma Enhanced Chemical Vapor Deposition (PECVD) for semiconductor manufacture, and pertains more particularly to methods and apparatus for generating and maintaining a uniformly-charged plasma in a reactor without requiring extensive metal-from-metal insulation.
In the field of Thin Film Technology, used extensively in manufacture of integrated circuits, requirements for thinner deposition layers, better uniformity over larger surfaces, and larger production yields have been, and are, driving forces behind emerging technologies developed by equipment manufactures. As semiconductor devices become smaller and faster, the need for greater uniformity and process control of film properties such as layer thickness, uniformity, and the like rises dramatically.
Various technologies are well known in the art for applying thin films to substrates in manufacturing steps for integrated circuits (ICs). Among the more established technologies available for applying thin films is Chemical Vapor Deposition (CVD), which includes Plasma Enhanced Chemical Vapor Deposition (PECVD). These are flux-dependent applications requiring specific and uniform substrate temperature and precursors (chemical species) to be in a state of uniformity in the process chamber in order to produce a desired film of uniform thickness on a substrate surface. These requirements become more critical as substrate size and device size increases, creating a need for more complexity in chamber design and gas flow techniques to maintain adequate uniformity.
CVD systems use a variety of known apparatus for delivering precursor gases to target substrates. Generally speaking, gas delivery schemes for CVD and PECVD processes are designed specifically for one particular application and substrate size. Therefore variations in theme of such delivery apparatus and methods will depend on the particular process parameters and size of substrates being processed in a single reactor. Prior art gas manifolds and diffusers have been manufactured from a variety of materials and are widely varied in design. For example, some gas delivery manifolds are long tubes that are either straight or helical with a plurality of small, often differently sized, gas delivery holes spaced longitudinally along the manifold. Most diffusers and showerheads are basically baffle-type structures having a plurality of holes placed in circular or spiral type arrangements on opposite facing plates or surfaces. Often the holes are contained in a series of expanding radii circles on each plate. Often such apparatus is adapted only for one type of process and cannot be used with other processes using the same CVD equipment.
One characteristic that is generally required in CVD gas delivery apparatus is that hole sizes and spacing between the holes is strictly controlled such that a uniform gas distribution or zone is maintained over a particular surface area. Uneven gas flow often results if some holes are inadvertently made too large in comparison with a mean size, or placed in wrong positions. If a larger substrate is used in a same or different chamber, then the gas delivery apparatus must often be exchanged for one that is designed and adapted for the variance in substrate size and/or chamber parameters. Improvements made to manifold and diffuser designs depend largely on empirical methods in the field resulting in numerous cases of product expenditure through batch testing.
One problem with many diffusing showerhead systems relates to limited gas flow dynamics and control capability. For example, gas delivered through a typical showerhead covers a diffusion zone inside the chamber that is produced by the array of diffusion holes placed in the showerhead. If a system is designed for processing a 200-mm wafer or wafer batch, the gas diffusion apparatus associated with that system will produce a zone that is optimum for that size. If the wafer size is increased or reduced beyond the fixed zone capability of a particular showerhead, then a new diffusion apparatus must be provided to accommodate the new size. There are typically no conventions for providing more than a few zones or for alternating precursor delivery for differing size substrates in one process.
In an environment wherein different sizes of substrates are commonly processed, it is desired that diffusing methods and apparatus be more flexible such that multi-zone diffusing on differing size substrates is practical using one showerhead system. This would allow for less downtime associated with swapping equipment for varying situations, and better uniformity by combining and alternating different zones during diffusion.
A gas diffusing system known to the inventor provides multi-zone (target zone) gas diffusing capability for CVD and PECVD systems. Zone-independent gas-supply lines integrated with the system allow process operators to adjust gas flow to each created target zone. A plurality of physical gas zones provided and contained in the diffuser assembly may be used alternately, in unison, or in specific combinations such that deposition uniformity is enhanced and may be fine-tuned during process.
The multi-zone diffuser known to the inventor uses an upper diffusing component, a gas transition component, and a lower diffusion component. All three components cooperate to provide a uniform layering capability that is consistent from process to process and batch to batch. The diffuser also is flexible to variances in substrate size by virtue of adding or subtracting physical gas zones in the diffuser thereby affecting target zones in the reactor.
As described above, PECVD has certain advantages over stock CVD applications because of a higher reactive state of precursor, which is charged by an RF plasma electrode. In standard CVD, plasma is sometimes used, not as a precursor, but for enhanced cleaning operations between deposition processes.
In PECVD, it is desired that a constant uniform state of charged plasma be maintained for enhancing reactivity for deposition and, of course, chamber cleaning. As with gas introduction, it is important that plasma is uniformly generated for the purpose of providing a uniform precursor reaction. If plasma is not uniform in generation than precursor will not react uniformly over a target, and may act to actually disturb otherwise uniform layering. In generating the plasma, it is desired that bombardment of precursor be directed in an effective manner to enhance uniformity.
In prior art applications the diffuser assembly or showerhead itself is used as the electrode for plasma charging and RF power is applied directly. This method requires extensive insulation steps in order to isolate the desired component acting as the electrode from the rest of an assembly. Also, typical gas diffusion apparatus has have large cavities to allow the gas to diffuse, and these areas can be susceptible to striking a plasma which is undesirable.
As a result of the above, insulating components, such as rings, plates and so on must be placed between metal components. Moreover, the component acting as the RF electrode is, most often, not physically designed to optimize plasma generation in the chamber.
What is clearly needed is a modular apparatus and method for generating and maintaining a uniform charged plasma in a PECVD or CVD process that requires minimum metal-from-metal insulation procedures. Such a system would enhance uniform plasma reactivity in process and facilitate expeditious maintenance operations between processes.
In a preferred embodiment of the present invention an RF electrode module for use with a gas-diffuser showerhead device in a CVD chamber is provided, comprising an electrically-conductive electrode ring with a ring inside diameter (R-ID) and a ring outside diameter (R-OD), the ring having an upwardly-extending power post, and an internal water-cooling channel open to an upwardly extending inlet tube and an upwardly-extending outlet tube, all posts and tubes parallel to a central axis of the ring; and an electrical-insulator ring having an insulator outside diameter (I-OD) equal to or greater than the R-OD and an insulator inside diameter (I-ID) equal to or smaller than the R-ID, and through-openings extending in the direction of the central axis of the ring and spaced such that the power post, inlet tube, and outlet tube extend through the through-openings in the insulator ring, the I-ID sized to engage a shoulder diameter of the gas diffuser showerhead device.
In a preferred embodiment electrode module has an angled face from the R-OD to the R-ID, facing toward the central axis of the electrode ring, and the electrical-insulator ring has a groove enclosing the electrode ring leaving only the angled face exposed. Also in a preferred embodiment the inlet post and the outlet post each comprise a groove in the outer tube diameter adjacent an end away from the electrode ring, the grooves for matching flexible extensions of split, threaded nuts capable of slipping over the end of the tubes such that the flexible extensions engage the grooves in the tubes.
In another aspect of the invention a split, threaded nut for engaging, a tube to connect a fluid supply is provided, the nut comprising a substantially cylindrical body having an outside major diameter and a through-bore along a central axis of the body, the through-bore defining an inside major diameter, the body having a length in the direction of the central axis, a tool interface at a first end of the body, the tool interface shaped to engage a tool for exerting a torque around the central axis, a threaded region along the outside major diameter from a second end of the body opposite the first end and extending from the second end along a substantial portion of the outside major diameter toward the tool interface, an internal ridge in the substantially cylindrical body extending from the inside major diameter toward the central axis for a portion of the length within the threaded region; and three or more flexible portions formed by cuts through the substantially cylindrical body from the second end extending for a substantial portion of the threaded region.
In some embodiments of the invention the internal ridge is in a trapezoidal shape, which provides surfaces in the transverse direction of the tube to absorb forces from internal fluid pressure.
In another aspect the electrode module further comprises a threaded nut assembled to each inlet and outlet tube, and each threaded nut has a substantially cylindrical body having an outside major diameter and a through-bore along a central axis of the body, the through-bore defining an inside major diameter, the body having a length in the direction of the central axis, a tool interface at a first end of the body, the tool interface shaped to engage a tool for exerting a torque around the central axis; a threaded region along the outside major diameter from a second end of the body opposite the first end and extending from the second end along a substantial portion of the outside major diameter toward the tool interface; an internal ridge in the substantially cylindrical body extending from the inside major diameter toward the central axis for a portion of the length within the threaded region; and three or more flexible portions formed by cuts through the substantially cylindrical body from the second end extending for a substantial portion of the threaded region. The threaded nut on each inlet and outlet tube engages the groove in the outer tube diameter by the internal ridge in the substantially cylindrical body of the threaded nut.
In yet another aspect a connector system for connecting a fluid supply apparatus to a tube having an external groove adjacent an open end, such that the fluid supply apparatus will remain in place against substantial internal fluid pressure is provided, comprising a nut having a bore and a length, an internal ridge in the bore orthogonal to the bore, an external thread over a portion of the length, and plural flexible regions formed by splitting the nut along a portion of the length, and an internally threaded connector hermetically joined to the fluid supply apparatus. The flexible portions, by flexing outwardly, allow the nut to be engaged over the tube and moved in the direction of the bore until the internal ridge engages the external groove in the tube, and wherein threading the external thread of the nut into the internally-threaded connector joins the tube to the fluid supply apparatus and constrains the flexible portions to hold the internal ridge in the tube groove such that the nut may not move along the tube.
In still another aspect method for attaching a fluid supply apparatus to an open-ended tube in a manner to retain the fluid-supply apparatus in place on the tube against substantial fluid pressure is provided, comprising steps of (a) forming a groove in the outer diameter of the tube adjacent the open end, (b) engaging a nut having a bore and a length, an internal ridge in the bore orthogonal to the bore direction, an external thread over a portion of the length, and plural flexible regions formed by splitting the nut along a portion of the length over the tube, until the internal ridge engages the groove in the tube; and (c) threading the external thread of the nut into an internal thread of a connector joined hermetically to the fluid-supply apparatus, thereby constraining the flexible regions such that the nut may not move along the tube.
For the first time, with this invention, in individual ones of several embodiments taught in enabling detail below, a separate internal electrode for establishing a plasma in a CVD chamber is provided to be used, if needed, with a gas diffusion showerhead apparatus, and a means of assembling the electrode mechanism to a chamber from inside the chamber, while providing a secure, yet removable connection for fluid feed tubes to the electrode is also provided.